This invention is an improvement on the inventions described and claimed in U.S. Pat. Nos. 4,588,773 (Federl et al I) and 4,775,716 (Kipouras et al or Federl et al II) and U.S. Pat. No. 4,857,590 (Gaggar et al), all of which are assigned to the predecessor of the present application's assignee.
Federl et al I relates to the use of an ABS graft copolymer containing an antistatic agent consisting essentially of a copolymer of epichlorohydrin and an oxirane composition, ethylene oxide. Federl et al II, a continuation-in-part of Federl et al I, also concerns an antistatic graft ABS, but one which contains smaller amounts of an epichlorophyorin/oxirane copolymer having a somewhat higher ratio of ethylene oxide to epichlorohydrin in said copolymer. U.S. Pat. No. 4,857,590 (Gaggar et al) is directed to the use of an alkyl methacrylate polymer to compatibilize the antistatic composition with the ABS polymer.
U.S. Pat. No. 4,719,263 (Barnhouse et al), discloses that the antistatic properties of various polymers may be improved by adding a copolymer of epichlorohydrin and ethylene oxide.
In U.S. Pat. No. 4,315,081 (Kobayashi et al) there is described a graft polymer containing an anionic surfactant to render the base resin antistatic. This patent is directed to specific graft polymers in which the rubbery backbone or trunk is a copolymer of a conjugated diene and a polyalkylene oxide monomer, although conventional ABS examples are given as controls. These polymers are purportedly rendered antistatic by the incorporation of up to about 5 wt.% of an anionic surfactant. A feature distinguishing Kobayashi from the present invention is that in the former, the surfactant is the only ingredient added for the promotion of antistatic properties. Moreover, since the test method described in the specification is not widely recognized, it is not possible to determine the absolute value of the antistatic properties attainable.
In the Gaggar et al patent, it was pointed out that certain properties such as tensile strength, heat distortion temperature and modulus are adversely affected by the introduction of the epichlorohydrin/ethylene oxide copolymer. Even the lower levels of loading described in the Federl et al II patent result in poorer physical properties. The use of an alkyl methacrylate polymer, such as poly (methyl methacrylate) promotes the compatibility between the base polymer and the copolymer.